harm in what way? unprotected sex comes with many risks, even protected sex has a slim chance of pregnancy. magickally it can conjure up much energy and make for powerful spells but i don't know if the actual focus is their to make spell casting possible. there are those 'great rite' rituals some people do. [physically or symbolically] sex magick is like any form of magick, it can backfire, but unlike many other forms you do have some health risks to consider.